To define the role of taurine in the heart we propose: (A) to deplete the heart of taurine, determine what functional deficits follow, then supply taurine in an attempt to restore function to normal; and (B) to determine what effects on heart function follow raising heart taurine levels above normal. Taurine, an amino acid-like compound present in all mammalian heart tissues, has been found (1) to antagonize epinephrine-induced premature ventricular contractions in dogs, (2) to accumulate in the left ventricular myocardium in human congestive failure and in the right ventricle of dogs with induced right heart failure, and (3) to show a high degree of correlation between its mean ventricular concentration and the mean heart rate in 12 different species (1) We have found it possible to lower taurine levels in the hearts of rats and mice by giving high doses of beta alanine (a carboxylic acid analgesic of taurine) (2) and of glucose (3). We will try to confirm in rats and mice the report that potassium deficient diets also lower taurine (4) To determine heart function we plan to use oscillographic and pen-writing EKG equipment and to use electrolytes like BaCl2 and BaCl2 to induce arrhythmias. The effects of producing supranormal heart taurine levels by giving high doses of taurine or mercaptoethylamine will also be studied. It is important to clarify the role of taurine in the heart as a potentially useful, naturally occurring, anti-arrhythmic principle.